ceph-fuse: return EINVAL if get invalid fino instead of assert

ceph-fuse: return EINVAL if get invalid fino instead of assert

All the snap ids of the finos returned to libfuse from libcephfs
will be recorded in the map of 'stag_snap_map', and will never be
erased before unmounting. So if libfuse passes invalid fino the
ceph-fuse should return EINVAL errno instead of crash itself.

Fixes: https://tracker.ceph.com/issues/54653
Signed-off-by: Xiubo Li <xiubli@redhat.com>
(cherry picked from commit a6e83d8dece53d11d0753f4843a6235eb1bb9834)